The present invention relates generally to motors and motor drivers, and more particularly to motors and solid state drivers for the same.
Various types of motors, such as brushless dc motors, have multiple phase windings and are operated by driving current pulses through the phase windings over a time interval which is contingent on rotation of the rotor. The motor can be controlled through variation of the effective value of the current pulses.
FIG. 1 is a simplified block schematic of a conventional motor control system. As with the other figures provided herein, the purpose of FIG. 1 is not to illustrate in detail the total construction of a complete motor-control system, but rather to illustrate roughly how particularly essential components of such a system co-act with one another. Consequently, the main purpose of the arrows drawn between the various blocks of the block schematic is to illustrate the flow of information and pulses between these components, rather than to denote the number of electric conductors used to interconnect the components in practice. Since the block schematic relates to a three-phase motor (e.g. variable reluctance, induction, permanent magnet brushless, etc.), three parallel arrows, conductors or lines have been used in the majority of cases, in order to obtain a lucid and clear block schematic. It will be understood that the number of conductors may, in reality, be greater or smaller than that illustrated (depending, for example, on the type of motor, whether the motor is arranged in a delta configuration, wye configuration, etc.).
In the exemplary embodiment, the brushless dc motor 1, which in the block schematic has the form of a variable reluctance motor, has three phase windings Axe2x80x2, Axe2x80x3; Bxe2x80x2, Bxe2x80x3; and Cxe2x80x2, Cxe2x80x3. The motor is driven by a motor driver circuit 5, which sends pulse-width modulated (PWM) current pulses to the phase windings from corresponding outputs A, B and C. The motor driver circuit 5 may, for instance, have double power stages, in a known manner, with switching transistors (not shown) for each phase. A power source (not shown) incorporates an energy source such as a battery.
The frequency and duration of the current pulses delivered to the phase windings from the motor driver circuit 5 are controlled with driving pulses delivered to the motor driver circuit 5 from a control unit 6. The control unit 6 receives from position sensors 7 information concerning the rotational angle of the rotor of the motor 1. The control unit 6 uses the information from the position sensors 7 to commutate the motor windings. Commutation is the periodic application of current to the proper windings as a function of rotor position in order to allow the motor to rotate with maximum torque. For example, three position sensors 7 of a known kind may be arranged in connection with respective phases in a manner known per se. On the other hand, any known position sensing scheme may be applied as will be appreciated.
The control unit 6 also receives information relating to motor current, i.e. the currents supplied to the phase windings of the motor 1, with the aid of sensors 8. Such information may be used by the control unit 6 to control the speed and/or torque of the motor 1. The sensors 8 may comprise three known sensors, and are arranged in connection with the lines to the phase windings, for example, in a manner known per se. Finally, the control unit 6 also receives control information from an external information source 9. The external information source may, for instance, be constructed to deliver information concerning a set point value relating to motor speed. The control unit 6 is constructed to vary the driving pulse parameters in response to information received from the sensors and from the external information source, for example to vary the pulse width, frequency, effective value and phase position of the driving pulses in relation to the angular position of rotor rotation, in order to achieve a desired motor speed at different operating conditions. In some applications, either the position sensors 7 or the current sensors 8 may be omitted. Each are included herein to illustrate the more general case but are not essential to the invention.
Certain applications require motor control systems which operate at relatively high power levels. In such applications, it has been conventional to configure two or more motor driver circuits 5 in parallel to increase the overall power deliverable to the windings of the motor 1. For example, FIG. 2 illustrates a conventional high power motor control system for driving the motor 1. As is shown, multiple motor driver circuits 5 (e.g., motor drivers #1, #2 and #3) have their respective outputs tied in parallel and coupled to the respective windings of the motor 1. Likewise, the respective inputs of the motor driver circuits 5 are coupled in parallel to the control unit 6. As a result, the motor driver circuits 5 provide identical PWM current pulses to each of the respective phases of the motor 1. In the case where there are three motor driver circuits 5 in parallel, for example, the overall power deliverable to the windings of the motor 1 is increased by a factor of 3.
The conventional high power motor control configuration represented in FIG. 2 may be suitable in many high power applications. There are, however, various shortcomings with such parallel design. For example, the motor driver circuits 5 will draw a substantially larger amount of current from the power source. Moreover, significant electromagnetic interference (EMI) can be generated by the multiple motor driver circuits 5 via the switching transistors, etc., compared to a single motor driver circuit 5.
In view of such types of shortcomings associated with conventional motor control systems, there is a strong need in the art for an improved motor control system. For example, there is a strong need in the art for a motor control system capable of delivering high power yet which minimizes the amount of current drawn from a power source. In addition, there is a strong need in the art for a motor control system that provides reduced EMI even in high power applications.
A controller for a motor such as a brushless dc motor is provided. The motor includes N redundant M-phase rotor/stator combinations (where N and M are both integers greater than 1). The controller includes N driver circuits each having M outputs. Each of the M outputs of a respective one of the N driver circuits provides pulse-width modulated (PWM) current pulses to a corresponding phase winding in a respective one of the redundant M-phase rotor/stator combinations. Furthermore, the controller includes a control unit operatively coupled to the N driver circuits for providing phase spacing between the N driver circuits. As a result, current pulses provided by the N driver circuits to a same phase winding in each of the redundant M-phase rotor/stator combinations are offset in phase.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.